Process for the selective hydrogenation of unsaturated compounds

ABSTRACT

The selective hydrogenation of unsaturated compounds which carry reducible groups containing nitrogen succeeds in a homogeneous phase with the preservation of the reducible groups containing nitrogen, characterized in that a compound of the formula 
     
         RuH.sub.2n L.sub.5-n 
    
     is used as a catalyst, in which 
     L signifies a phosphane or arsane and 
     n signifies 1 or 2.

This is a continuation of application Ser. No. 928,196 filed Nov. 7,1986, abandoned.

The invention concerns a process for the selective hydrogenation ofunsaturated, optionally high-molecular compounds which carry reduciblegroups containing nitrogen.

It is known that C--C-double bonds can be hydrogenated selectively onsolid catalysts in presence of reducible groups containing nitrogen. Forthis purpose palladium or platinum catalysts are used. Yields of up to90% are achieved by this means (Houben-Weyl, Methoden der OrganischenChemie, Volume IV, 1c, Reduction I (1980), page 168). The selectivityis, however, frequently unsatisfactory. Thus in using platinum oxide forthe hydrogenation of 1-cyano cyclohexene only 31% of the desired cyanocyclohexane is obtained (cf. M. Freifelder, Practical CatalyticHydrogenation, (1971), page 157).

A method of hydrogenating unsaturated nitriles using rhodium complexesas homogeneous catalysts (Wilkinson-complex) is also known. The cyanogroup is not hydrogenated in this process. As a result of ligandexchange, however, the catalyst can be deactivated with nitriles (cf.Houben-Weyl, loc. cit., pages 57 to 60).

As rhodium complexes of the formula [(C₆ H₅)₃ P]₃ Rh^(I) X are alsosuitable for the hydrogenation of nitriles (DE-AS 1 793 616), it can beexpected that the selectivity is not always adequate for thehydrogenation of olefinic double bonds in presence of nitrile groups.

It is known from U.S. Pat. No. 3,454,644 that it is possible tohydrogenate keto-, formyl-, nitrile-, nonaromatic --C═C and --C═C-groupswith complexes of the L_(n) MX₂ type containing phosphane (L=CO ortertiary phosphane, n=3 or 4, M=ruthenium or osmium, X=halogen and/orhydrogen) whereby all the groups of this type which are present arealways hydrogenated.

Cationic ruthenium complexes which are suitable as homogeneous catalystfor the hydrogenation of olefines in acidic, methanolic solution, aredescribed in J. C. S. Dalton 1973, pages 846 to 854. No hydrogenation ofinterior positioned double bonds takes place with these complexes.

The selective hydrogenation of polymeric unsaturated compounds whichcarry reducible groups containing nitrogen is particularly problematicsince it is not possible to separate off by-products in this case or, atleast, only with extremely great expenditure.

A method of hydrogenating CC-double bonds of diene-(meth)acrylonitrilecopolymers with a large proportion of alternating diene nitrile unitshomogeneously with rhodium halogen complex catalysts in chlorobenzene isknown from U.S. Pat. No. 3,700,637. The suitability of other metals suchas platinum, ruthenium, iridium, palladium, rhenium, cobalt or copper,homogeneously or heterogeneously, is indicated.

In DE-OS No. 2 539 132 a selective hydrogenation of butadieneacrylonitrile copolymers which is dependent on a solvent, with the knownrhodium catalyst is postulated, in which the CN-triple- and cis-doublebonds are preserved and the vinyl and trans-double bonds arehydrogenated quantitatively if chlorobenzene is used as the solvent. Inother solvents, in particular ketones, only low hydrogenation rates areachieved.

Finally, DE-OS No. 2 459 115 gives a method of homogeneously or,preferably, heterogeneously hydrogenating unsaturated polyhydroxyhydrocarbons with molecular weights of up to 4000 with the preservationof the hydroxyl groups with the aid of ruthenium catalysts. Aliphatichydrocarbons, aromatic hydrocarbons, alcohols, ethers, esters and waterare used solvents for the heterogeneous hydrogenation process; nodetails are given of the homogeneous hydrogenation process. The polymerscan apparently also contain, for example, acrylonitrile, as a comonomer,but no detailed descriptions are given, although it must be borne inmind that it is known from U.S. Pat. No. 3,454,644, example IX, that thenitrile group of benzonitrile is hydrogenated, in homogeneousRu-catalysis in ethanol, to the amino group.

As the occurrence of rhodium is very small and rhodium is not only usedin the chemical industry but primarily in the electrical industry, theglass industry and the ceramics industry and, most recently, especiallyin the motor car industry (exhaust catalysts), the possibility of ashortage of this precious metal in the future cannot be ruled out.

The object of the present invention was to provide a new homogeneoushydrogenation process, independent on rhodium, for the selectivehydrogenation of unsaturated compounds which carry reducible groupscontaining nitrogen, which also makes it possible for polymericunsaturated compounds which carry reducible groups containing nitrogento be hydrogenated with the preservation of the reducible groupscontaining nitrogen.

The object was achieved, surprisingly, by the homogeneous reactionprocess with the use of special rutheniumhydrido phosphane complexes.

The invention provides, therefore, for the hydrogenation of unsaturatedcompounds which carry reducible groups containing nitrogen, in ahomogeneous phase, with the preservation of the reducible groupscontaining nitrogen, characterised in that a compound of the formula

    RuH.sub.2n L.sub.5-n

is used as a catalyst, whereby

L signifies phosphane or arsane and

n signifies 1 or 2.

The phosphanes and arsanes preferably correspond to the formulas##STR1## in which R₁, R₂ and R₃ can be the same or different and cansignify alkyl, aryl, cycloalkyl and aralkyl.

Examples of alkyl residues are straight-chain or branched, saturatedhydrocarbon residues with 1 to 20, preferably 1 to 12, in particularpreferably 1 to 6 C-atoms.

Cycloalkyl residues are, for example, cyclic, saturated hydrocarbonresidues with 5 to 7 C-atoms.

Aryl residues are, for example, aromatic hydrocarbon residues from thebenzene series with 6 to 18, preferably 6 to 10 C-atoms.

Aralkyl residues are, for example, alkyl residues substituted by aryl,which consist of a striagth-chain or branched hydrocarbon residue with 1to 6 C-atoms in the aliphatic part, and of a residue of the benzeneseries, preferably phenyl, in the aromatic part.

The alkyl-, cycloalkyl-, aryl-, and aralkyl residues described above canoptionally be substituted by hydroxy, C₁ - to C₆ -alkoxy, C₁ - to C₆-Carb-C₁ -C₄ -alkoxy, fluorine, chlorine or Di-C₁ -C₄ -alkyl aminogroups and the cycloalkyl-, aryl- and aralkyl residues can also besubstituted by C₁ - to C₆ -alkyl, Alkyl-, cycloalkyl- and aralkyl groupscan contain keto groups.

As ligands L e.g. triphenyl phosphane, diethyl phenyl phosphane,tritolyl phosphane, trinaphthyl phosphane, diphenyl methyl phosphane,diphenyl butyl phosphane, tris-(p-carb methoxy phenyl)- phosphane,tris-(p-cyano phenyl)-phosphane, tributyl phosphane, tris-(trimethoxyphenyl) phosphanes, bis-(trimethyl phenyl)-phenyl phosphanes,bis-(trimethoxy phenyl)-phenyl phosphane, trimethyl phenyl-diphenylphosphanes, trimethoxy phenyl diphenyl-phosphanes, tris(dimethoxyphenyl)-phosphanes, bis-(dimethyl phenyl)-phenyl phosphanes,bis-(dimethoxy phenyl)-phenyl phosphanes, dimethyl phenyl diphenylphosphanes, dimethoxy phenyl diphenyl phosphanes, diphenyl-trifluoromethyl phosphane, triphenyl arsane, ditolyl phenyl arsane,tris-(4-ethoxy phenyl)-arsane, diphenyl cyclo hexyl arsane, dibutylphenyl arsane and diethyl phenyl arsane may be used.

Triaryl phosphanes, in particular triphenyl phosphane, are preferred.

Some of the complexes used are known. They can be prepared, for example,from ruthenium dichloride-tris-triphenyl phosphane by reduction. (J.Organomet. Chem. 54, (1973) 259-264).

Nitriles, imines and oximes, for example, are used as unsaturatedcompounds which carry reducible groups containing nitrogen of whichnitriles are preferred.

High-molecular, unsaturated compounds which carry reducible groupscontaining nitrogen are preferably copolymers containing nitrile groupsof 85 to 50% by weight, preferably 82 to 55% by weight, at least of aconjugated diene, 15 to 50% by weight, preferably 18 to 45% by weight,at least of an unsaturated nitrile and 0 to 10% by weight, preferably 0to 8% by weight, at least of another monomer which can be copolymerizedwith conjugated dienes and unsaturated nitriles.

For example, buta-1,3-diene, 2-methyl buta-1,3-diene, 2,3-dimethylbuta-1,3-diene and penta-1,3-diene are used as conjugated dienes, andacrylonitrile and methacrylonitrile are used as unsaturated nitriles.

Vinyl aromatic substances such as styrene, o-, m- or p-methyl styrene,ethyl styrene, vinyl naphthalene and vinyl pyridine, α,β-unsaturatedmono carboxylic acids with 3 to 5 C-atoms such as acrylic acid,methacrylic acid and crotonic acid are used as other monomers, as wellas α,β-unsaturated dicarboxylic acids with 4 to 5 C-atoms such asmaleic, fumaric, citraconic and itaconic acid, as well as vinyl alkylether with 1 to 4 C-atoms in the alkyl portion.

Preferably, a binary copolymer made of butadiene and acrylonitrile ishydrogenated.

The molecular weight of the polymers is not critical and is between 500and 500 000 g per mol, preferably between 1000 and 200 000 g per moland, in particular, between 30 000 and 150 000 g per mol (numberaverage, determined by gel permeation chromatography).

The conversions or the degrees of hydrogenation, resp., (percentage ofhydrogenated CC-double bonds related to the total number of theCC-double bonds which were originally present in the polymer) can be upto 100%. The hydrogenation process can, however, be interruptedbeforehand if necessary. Polymers with degrees of hydrogenation of over80%, in particular of over 90%, preferably of over 95% are preferablyprepared according to the process of the invention. The degree ofhydrogenation is determined by means of IR-and NMR-spectroscopy.

In particular, low-molecular ketones with 3 to 10 C-atoms, in particularacetone, butanone, pentanones, cyclopentanone and cyclohexanone are usedas solvents for the hydrogenation process.

The concentration of the unsaturated compound, related to the totalsolution, is 1 to 90, preferably 5 to 40% by weight.

The concentration of catalyst, related to unsaturated compound(calculated as ruthenium), is 10 to 1000, preferably 10 to 600 ppm, morepreferably 40 to 500 ppm.

The hydrogenation process is preferably carried out at 80° to 200° C.,preferably at 100° to 180° C., in particular at 115° to 160° C. and 1 to350 bar, preferably at 20 to 250 bar hydrogen pressure.

The catalyst can be separated off after the reaction by the usualmethods and the product purified, for example, by distillation orcrystallization.

In the case of a high-molecular compound the polymer is separated offfrom the solution using the usual methods, for example, by means ofevaporation, by the injection of water vapour or by the addition of anonsolvent. A drying process follows for the removal of residual solventor water.

The polymers hydrogenated according to the invention are hardened in theusual manner by means of a peroxide or sulphur vulcanization, providedthat the vulcanization is not carried out by cross-linking byirridation.

Because of their excellent weather resistance, ozone resistance, oilresistance and hot air resistance, as well as resistance to a coldclimate, these polymers can be used for high-grade rubber articles, suchas seals, hoses, membranes, for cable insulations and cable coverings.

The low-molecular compounds hydrogenated according to the inventionwhich carry reducible groups containing nitrogen, are valuableintermediate products for the preparation of active ingredients.

EXAMPLE 1

A solution of 220 g of statistical butadiene acrylonitrile copolymerwith 34.9% by weight acrylonitrile, having a Mooney viscosity of ML 1+4(100° C.) of 29 in 1800 ml butanone, which solution had been carefullypurged with nitrogen, was placed in a 3-liter autoclave under nitrogenpurging. Keeping the atmosphere inert a solution of 590 mg RuH₄ (PPh₃)₃in 200 ml butanone which had also been purged with nitrogen was added,and a pressure of 80 bar hydrogen was applied. The mixture was heated to130° C. and then the reaction was continued at 140 bar hydrogen pressurefor 4 hours at 130° C. The degree of hydrogenation of the polymer wasdetermined using NMR- and IR-spectroscopy to be 95%.

EXAMPLE 2

According to the instructions in example 1, a hydrogenation process wascarried out with 550 mg RuH₂ (PPh₃)₄. The degree of hydrogenation of thepolymer was 97% after 6 hours of reaction time.

We claim:
 1. A process for the hydrogenation of the C═C double bonds ofa polymer consisting essentially of(i) 85 to 50% by weight ofcopolymerized units of conjugated dienes selected from the groupconsisting of .[.butadiene-1.3 and pentadiene-1.3,.]..Iadd.butadiene-1.3, pentadiene-1.3, 2-methylbutadiene-1.3 and2,3-dimethylbutadiene-1.3 .Iaddend. (ii) 15 to 50% by weight ofcopolymerized units of unsaturated nitriles selected from the groupconsisting of acrylonitrile and methacrylonitrile, and (iii) 0 to 10% byweight of copolymerized units of other copolymerizable monomer in ahomogeneous phase up to a hydrogenation degree of more than 80% withpreservation of the nitrile units, which process comprises reacting thepolymer with hydrogen to a degree of hydrogenation greater than 80% at apressure from 1 to 350 bar and a temperature from 80° to 200° C. in aketone solvent having 3 to 10 carbon atoms in the presence of 10 to1,000 ppm catalyst, based on polymer, which is a compound of the formula

    RuH.sub.2n L.sub.5-n

wherein L is of the formula ##STR2## wherein R₁, R₂ and R₃ are the sameor different and each is alkyl having 1 to 20 carbon atoms, cycloalkylhaving 5 to 7 carbon atoms, aryl having 6 to 18 carbon atoms or aralkylhaving 1 to 6 alkyl carbon atoms, and n is the integer 1 or
 2. 2. Aprocess according to claim 1, characterised in that triaryl phosphanesare used as ligands L.
 3. A process according to claim 1, characterisedin that triphenyl phosphane is used as ligand L.